Although much is known about the structure and biochemistry of muscle, two outstanding problems remain unsolved: 1) the mechanism of energy transduction during contraction, and 2) the mechanism of calcium regulation. Current theories on these topics often invoke two phenomena: 1) conformational changes in the contractile proteins. There had, however, been very few experimental demonstrations of such phenomena. Fluorescence probes can be gainfully employed in this respect. Fluorescence probes that are polarity sensitive can be used as reporters of conformational changes. Measurements of energy transfer between pairs of fluorescence probes can be used to map the distances between the contractile proteins, and to detect changes in these distances. Thus, one may use such methods to detect and characterize the conformational changes and protein-protein movements in the contractile proteins of muscle. Such information will be vital towards the construction of a "Unified Theory for Muscle Contraction."